If you look up close, you would be able to see grains of sand. From this distance you can see different layers from where the sand was laid down. This rock is sandstone. The sand grains are cemented together to make sandstone. Sandstone is a common type of sedimentary rock.

The main types of sedimentary rocks are clastic or chemical. Clastic sedimentary rocks are made of sediments. The sediments differ in size. Chemical sedimentary rocks are made of minerals that precipitate from saline water.

Clastic Sedimentary Rocks

Clastic sedimentary rocks
are grouped by the size of the sediment they contain. Conglomerate and breccia are made of individual stones that have been cemented together. In conglomerate, the stones are rounded. In breccia, the stones are angular. Sandstone is made of sand-sized particles. Siltstone is made of smaller particles. Silt is smaller than sand but larger than clay. Shale has the smallest grain size. Shale is made mostly of clay-sized particles and hardened mud.

Rock

Sediment Size

Other Features

Conglomerate

Large

Rounded

Breccia

Large

Angular

Sandstone

Sand-sized

Siltstone

Silt-sized, smaller than sand

Shale

Clay-sized, smallest

When sediments settle out of calmer water, they form horizontal layers. One layer is deposited first, and another layer is deposited on top of it. So each layer is younger than the layer beneath it. When the sediments harden, the layers are preserved.

Chemical Sedimentary Rocks

Sedimentary rocks formed by the crystallization of chemical precipitates are called
chemical sedimentary rocks
. Dissolved ions in fluids precipitate out of the fluid and settle out, just like the halite in
Figure
below
.

The evaporite, halite, on a cobble from the Dead Sea, Israel.

Living creatures can help chemicals become sedimentary rocks. Limestone is an example.